There are two major types of fossils - body fossils
and trace fossils. Both are the remains of living organisms. Body fossils
reveal the body structure of the organism while trace fossils reveal the activities
of these organisms.

The process of fossilization is called taphonomy.
There are three main components. First, there is the death of the organism.
Then, there are certain processes that can happen to the organism before it
is buried. These processes can include body decay due to natural elements such
as wind, water or attack from predators. Finally, there are certain processes
that occur after the organism's body is buried. These processes result in the
different categories of fossils.

What are some factors that can affect fossilization?

Body construction: Does the organism have hard or soft body
parts?

Environment: Do the surrounding conditions allow for rapid
burial and preservation? Will the body be exposed to many elements of erosion?

Predators: Are other organisms going
to destroy the body before it can be preserved?

How do fossils form?

There are many ways fossils can be formed including permineralization,
freezing, compression, and entrapment by amber. (See
informational links.) Methods of fossilization often involve rapid burial
in such a way that predators and erosional effects are eliminated. This allows
for preservation of the body parts or trace evidence. Below are some examples.

Permineralization is a major method that involves the hardening
of minerals that have entered the small pores and cavities of dead organisms.
As hard water (water containing minerals) enter these pores, minerals are deposited
and, under high pressures, becomes solid.

Natural molds and casts form when the hard parts (such as shells)
are buried in sediment leaving behind an impression of its shape. If the interior
of the shell were to be filled with sediment that hardened, an internal mold
would be created. However, if the shell should dissolve away over the years,
it will leave behind a mold of the shell (external mold).

How is fossilization dependent upon the environment?

The environment plays a crucial role in an organisms ability
to fossilize. The best scenario would be in which an organism is buried at the
bottom of a lake where it is then covered by a lot of sediment. In this type
of environment, the organism is protected from other animals and natural elements
that would cause the body's breakdown. It is crucial that the body be in an
environment that allows for rapid burial. Areas in which there is a high rate
of sediment deposition is ideal because of the presence of minerals and the
increase of pressure.

The environment can also affect where the fossil is found.
For example, river currents can carry a body away from the site of death before
it is buried.

Drier environments, such as land, are more susceptible to the
effects of erosion and so it is more difficult to preserve the organism before
it decays.

Where are fossils found?

Both body and trace fossils are commonly found buried in sedimentary
rocks. There are major sediment deposits in such places as the mouths of rivers
or at the bottom of sea and lake beds. Because rock layers are laid down oldest
at the bottom and youngest at the top, fossils can provide an important clue
to the Earth's history. (See info on the Fossil
Record.)

Fossils can be found in more unusual places as well, such as
inside amber or tar pits. Fossils can be found in many places around the world
provided the conditions are right.

What does fossilization tell us about the fossil record?

The fossil record does not represent all of the living things
once found on Earth. The reason for this is because not all organisms have correct
properties that allow for fossilization. Some organisms may have decayed before
fossilization could begin. Organisms that live on land or have soft body parts
are less likely to fossilize than those that live in water or have hard body
parts. Therefore, the fossil record can only provide a piece of Earth's history.